Earthmoving and construction work machines often employ hydraulic systems that provide functionality and control to various aspects of the machines. For example, some work machines employ a hydraulic braking system to control driving speeds and a fan hydraulic drive system that controls machine cooling.
Because each system may have separate flow requirements, the hydraulic systems on some work machines are isolated systems, each having a separate fluid pump. However, providing a separate pump for each separate hydraulic system may be redundant and may be cost prohibitive. In addition, such a system may require additional maintenance and upkeep. To overcome these disadvantages, some work machines combine or integrate certain hydraulic systems.
Even in a combined system, however, one hydraulic system may require different fluid flow parameters than the other and may require different fluid flow arrangements at different times. To address this, some known systems direct fluid from a common pump to one system or the other system using a cut-in/cut-out device. For example, on a conventional work machine having a combined braking system and a combined cooling system, fluid may be directed to the brake system to charge or fill accumulators with fluid. Then, the cut-in/cut-out device may cut-out fluid flow to the braking system and may instead direct fluid to the cooling system.
Such a conventional system combining a braking system and a cooling system is disclosed in U.S. Pat. No. 7,730,722 B2 to Williams ('722). The '722 patent is directed to a hydromechanical transmission (HMT) or hydrostatic transmission (HST) with a bypass valve. The '722 patent discusses adjusting the HMT ratio settings, depending on operator input, deceleration requirements and external loading due to application of brakes and/or terrain. To adjust the HMT ratio, '722 patent discloses a hydrostatic circuit having a first hydraulic kit that is fluidly connected to a second hydraulic kit via first and second fluid lines. The hydraulic circuit in '722 patent additionally has a bypass valve connected in parallel to the first and second hydraulic kits via the first and second fluid lines. The bypass valve is then controlled in such a way that the valve opens when a predetermined condition is met in order to relieve pressure in the hydrostatic circuit. However, the additional bypass valve connected in parallel to the first and second hydraulic kits involves additional costs and requires additional fluid lines which can make the HMT unnecessarily complicated. Moreover, when the bypass valve opens, the torque of the HMT is lowered regardless of the swash plate angle and the speed of the two hydraulic kits, and thus the efficiency of the HMT deteriorates.
As a result, there is a need for a hydraulic circuit fluidly connecting a plurality of machine components without complicating the circuit and losing its efficiency.